What are you going to use them for initially?

Earth to Alchemize for Money?
Nature to cast Mother Oak?
Nature to cast Gift of Health?
Forging Magic Items?
Earth to Summon Elementals?

It's very nearly as important to know where you are going with your Gem Income as to get it

For me how fast I need my gems and for what reason dictate how fast and how hard I search provinces. As most of the time I have to weigh my resources against research and expansion.